1. Field of the Invention
This invention relates to a process for the production of a foam inhibitor mixture consisting of hydrophobicized silica and paraffin hydrocarbons by reaction of hydrophilic silica dispersed in the paraffin hydrocarbons with alkyl chlorosilanes.
2. Discussion of Related Art
Foam inhibitor mixtures of paraffin hydrocarbons and hydrophobicized, i.e. silanized, silica are known and are widely used. One application known from European Patent 8 829 is in foaming detergents. However, it has been found that mixtures of paraffin hydrocarbons and hydrophobicized silica prepared beforehand often show only limited stability in storage which cannot be improved to the necessary extent even by blending.
In U.S. Pat. No. 3,388,073, it is proposed to prepare these mixtures "in situ", for which purpose the hydrophilic silica serving as starting material is dispersed in a liquid paraffin hydrocarbon, reacted with dialkyl dichlorosilane and the mixtures obtained directly used as such after removal of the hydrogen chloride. The alkyl groups in the dialkyl dichlorosilanes are said to contain no more than 4 carbon atoms and preferably consist of methyl groups. The hydrophilicized silica contains cyclic siloxane residues. It has been found that the foam-inhibiting properties of the mixtures obtained are inadequate for numerous applications, particularly high-foam surfactants and detergents.
In U.S. Pat. No. 4,082,691, it is proposed to carry out the reaction of the silica dispersed in the paraffin hydrocarbons in two stages, alkyl trichlorosilanes being used in the first stage and dialkyl dichlorosilanes in the second stage. The alkyl groups in these chlorosilanes may contain from 1 to 18 carbon atoms or may be cycloallphatic, although the dichlorosilanes preferably contain methyl groups while the trichlorosilanes preferably contain long-chain alkyl groups. The patent specification teaches that only a two-stage reaction with a molar ratio of dichlorosilane to trichlorosilane of from 1:1 to 1:5 leads to useful foam inhibitors. Molar ratios below or above this range lead to unsuitable foam inhibitors. In addition, the temperature of the reaction mixture on addition of the chlorosilanes should be below 50.degree. C., and preferably below 40.degree. C. The use of paraffin hydrocarbons, particularly microwaxes, which melt above that temperature is thus out of the question.
Therefore, an object of the present invention s to provide an "in situ" process for the production of mixtures of paraffin hydrocarbons and silanized silica which enables relatively high-melting paraffins characterized by a particularly good foam-inhibiting effect to be jointly used and which leads in a single-stage, and hence simplified procedure, to products having a superior foam-inhibiting effect.